Woop. 149 
CHAP. IL_VEGETABLE COMPOUNDS IN WHICH 
THE HYDROGEN AND OXYGEN ARE PRE- 
SENT IN THE PROPORTIONS IN WHICH 
THEY FORM WATER. 
1. woop. 
582. This forms the principal part of most vegetables. 
As we find it in trees, it contains many of the juices of the 
vegetable; by digesting any kind of wood in boiling water 
and then in alcohol these are removed, and the pure woody 
part remains, called woody-fibre or lignin. This is a fibrous 
substance destitute of taste and smell, and, if perfectly dry, 
_ not altered by exposure to the air. When moist it is de- 
composed, carbonic acid and water being produced. The 
same products result from its combustion. When exposed 
in close vessels to a strong heat it is resolved into acetic acid - 
(pyroligneous acid) mixed with an empyreumatic oil, car- 
bonic acid, carbureted hydrogen, water, and a fine charcoal 
— of the wood from which it is made. Lignin contains also a 
little carbonate of lime. It consists of carbon, oxygen, and 
hydrogen, in the following proportions, according to Dr. 
Prout :— 
* 
Carbon, : : : 50 
Oxygen; i i £ . 44,45 
Hydrogen, eer oe : 5.55 
100 parts. 
2. Gum. 
583. This substance exudes in a fluid form from certain 
trees, and soon becomes hard when exposed to the air. It 
is white, pale straw-coloured, or even colourless, transparent, 
tasteless and very brittle. It is very, 7 salable Sam 
